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<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <script>
        //var是定义变量的关键字
        var name = "xiaoming"; //字符串

        // alert(name);

        var age = 18;//数字
        // alert(age);

        var num = 3.5;//数字

        // alert(num);


        var isGood = false;//布尔类型

        // alert(isGood);
        //空 
        var student1 = null;
        // alert(student1);


        var hehe;  // undefined
        alert(hehe);


    </script>
</head>

<body>




</body>

</html>